Method and apparatus for testing aircraft structures



Aug. 28, 1945. P. H. KEMMER ET AL METHOD AND APPARATUS FOR TESTING AIRCRAFT STRUCTURES Filed Sept. 11 1939 '7 Sheets-Sheet l v -v4r-r0zs 8402. hi ffEMMA? EQGMP/Q /4 ,4 ER 5 '5 I By Aug- 28, 1945- P. H. KEMMER ETAL 2,383,491

METHOD AND APPARATUS FOR TESTING AIRCRAFT STRUCTURES 7 Sheets-Sheet 2 Filed Sept. 11, 1939 2404. h. AEMMEE 5064/? A. /4 41/5,

Afro/ave Vs Aug 28, 1945; P. H. KEMMER ET AL METHOD AND APPARATUS FOR TESTING AIRCRAFT STRUCTURES Filed Sept. 11, 1959 7 Sheets-Sheet 3 fivvl'lvfozs 1 44/4 H. KEMME/Q 5064/? P. WEAVER BY m ,dr' ra A/e'vs 3423, 5- P. H. KEMMER ETAL 2,383,491

METHOD AND APPARATUS FOR TESTING AIRCRAFT STRUCTURES Filed Sept. 11, 1959 7 Sheets-Sheet 4 PAM. ff. A EMME/P 5.064,? A? l fg4 fi"? 4 Arrom ws'rs ug. 28, 1945- P. H. KEMMER ET AL 2,383,491

METHOD AND APPARATUS FOR TESTING AIRCRAFT STRUCTURES Filed Sept. 11, 1939 'Z Sheets-Sheet 5 P. H. KEMMER ET AL METHOD AND APPARATUS FOR TESTING AIRCRAFT STRUCTURES Aug. 28, 1945.

Filed Sept. 11, 1939 7 Sheets-Sheet 6 M d roemevs Aug. 28, 1945. P. H. KEMMER ET AL.

METHOD AND APPARATUS FOR TESTING AIRCRAFT STRUCTURES 7 SheetsShee 7 Filed Sept. 11, 1939 TORI/E v s Patented Aug. 28, 1945 METHOD AND APPARATUS FOR TESTING AIRCRAFT STRUCTURES Paul H. Kemmer, Fairfield, and Edgar R. Weaver, Dayton, Ohio Application September 11, 1939, Serial No. 294,344

(Granted under the act of March 3, 1883, as amended April 30, 1928; 370 0. G. 757) 21 Claims.

The invention described herein may be manufactured and used by or for the Government for governmental purposes, without the payment to us of any royalty thereon.

This invention relates to an improved method and apparatus for static testing aircraft structures.

It is customary to subject airplane structures and various parts thereof to a static test to check resistance to bending and shear under basic or other loads.

In the past, test loads have been applied to airplane structures and the various parts thereof by means of bags of sand or shot. This method is time-consuming, laborious, and expensive, because many thousands of pounds of calibrated weights must be handled and placed. Furthermore, this method does not represent a true ap-' plication of the loads, and consequently the pressures, to which the plane and the various parts thereof, particularly the wings, are subjected during actual flight conditions. The reason for this is as follows: It is well established that the forces on an airplane wing comprise a positive pressure sustaining force on the underside of the Wing and a lifting force on the upper side of the wing, created by the flow of air pastthe wing. The flow of air past the wing results in a sub-atmospheric pressure adjacent the upper surface of the wing, commonly called negative pressure." The forces vary with the angle of attack, tests having shown that for typical wings at a zero degree angle of attack, 100% of the total upward force on a wing is derived from the upper surface; at a edegree angle of attack, 74% is due to the force on the upper surface; and at a ill-degree angle of attack, 68%.

There is also a variation of lift across the wing span because of the complex motion of the air in flowing around the wing. On the underside of the wing, near the tip, air is flowing out and upward, while nearer the center of the span, the outward component is not so pronounced. Similarly, the upper side of the wing is subjected to an inward component which is greatest at thetip. Thus, it is apparent that the pressure on the upper and lower wing surfaces are variable for different conditions of flight.

Prior to this invention, static testing of an airplane wing was accomplished by suitably anchoring and Supporting it at one end after the manner of a cantilever beam, loading the upper side with bags of sand or shot and measuring the deflections for different increments of load. It is readily appreciated that the stresses and strains developed in the wing and transmitted to the fuselage of the plane are different, when tested in this manner, from those developed under actual flight conditions.

It is an object of this invention to provide static test apparatus for loading an airplane, and particularly the wings thereof, in the same man- I ner as the airplane is loaded during various flight conditions, also to so locate and apportion the loads as to more perfectly simulate flight conditions than has been possible with known methods of loading during testing.

It is another object of this invention to provide, as a part of the testing apparatus, a lifting patch adapted to be temporarily cemented to a surface subjected to negative pressure" and which it is desired to subject to a tension force by a pull or lift.

It is a further object of this invention to provide a lifting patch which will develop a lifting force or negative pressure sufficiently large for the purpose intended and which can be applied over plate joints, rivets, curved surfaces and the like. It is of primary importance that the patch be capable of transmitting a pulling force of large magnitude while offering a negligible resistance to buckling of the tested member in the event of suflicient flexure to cause buckling.

It is still another object of this invention to provide static test apparatus which so nearly simulates loadings under actual flight conditions that the yield point and ultimate strength of the structure can be predicted from the stress strain and deflection data obtained by the test. In proof testing it is thus possible to test the plane itself rather than a test model, without injury to the plane.

It is a further object of this invention to produce an airplane and parts thereof which will comply with different design flight characteristics by subjecting the airplane to forces corresponding in magnitude, direction, and application to the forces exerted upon the airplane for the design flight characteristics, determining from the deflection, distortion, buckling, wrinkling, and failure of members, the lack of compliance with the design flight characteristics and modifying the structure accordingly.

It is also an object of this invention to sustain an airplane in a simulated flight condition and while in said sustained condition to subject it or a selected part thereof to a vibration test.

In carrying out the invention, the forces and pressures applied to each part or surface of the structure correspond in magnitude and direction to the forces and pressures to which the part or surface will be subjected during flight. For instance, a force equal to the engine load is applied to the plane at the center of gravity of the engine load. Similarly applied are gas tank, landing gear, pilot, and other loads.

The airplane may be tested under a condition of basic or special loads. The basic loads on an airplane are the loads applicable when the airplane is at rest or in a condition of unaccelerated flight. It is readily understood that when static testing under conditions other than that of basic load, it is necessary to additionally load or suitably anchor the airplane to provide a reaction load appropriately located and opposed in direction to the force constituting the special load condition. The special load condition may result from any one of the following conditions: The load applied during some special maneuver, the maximum probable load on the airplane or part, the design load or the ultimate load.

' In the drawings:

Fig. 1 is a perspective view of a test set-up showing apparatus for testing an airplane in accordance with the teachings of this invention.

Fig. 2 is a cross-sectional view of an airfoil section being tested by having a tension force applied to the upper surface and a partial sustaining force to the lower surface of the section.

Fig. 3 is a cross-sectional view along the lines 3--3 of Fig. 2.

Fig. 4 is a perspective view similar to Fig. 1, but showing vibration-producing apparatus associated with the plane.

Fig, 5 is a detail view of the connection of the lower beam member to the upper beam member showing the adjustability of the members to vary the ratio of the forces exerted by the upper and lower beams.

Fig. 6 is a plan view of an airplane wing showing an arrangement of lift-producing members.

Fig. 7 is a cross-sectional view taken along the lines 1-1 of Fig. 6, showing the force-apportioning lever system.

Fig. 8 is a cross-sectional view taken along the lines 8-8 of Fig. 6.

Fig. 9 is a cross-sectional view taken along the lines 9-9 of Fig. 6.

Fig. 10 is a cross-sectional view taken along the lines Ill-I0 of Fig. 6.

Fig. 11 is a perspective view of a lifting patch.

Fig, 12 is a cross section taken along the lines l2l2 of Fig. 11.

Fig. 12a is a view similar to Fig. 12, showing a modified form of lifting patch.

Fig. 12b is a view similar to Fig. 12a of a modifled form of the patch.

Fig. 13 is a perspective view of another type of lifting patch.

Fig. 14 is a cross section taken along the lines 14- of Fig. 13.

Fig. 14a is a view similar to Fig. 14 of a modified form of the patch.

Fig.15 is a cross-sectional view showing how the patch permits buckling of the surface of the airfoil.

Fig. 16 is a plan view showing a conduit arrangement for conducting actuating fluid from a common source of power to the force-producing members.

Fig. 17 is a plan view similar to Fig. 16 showing pressure-controlling and -indicating means incorporated in the system;

Fig. 18 is an elevational view of an alternative type of jack.

Fig. 19 is an isometric view of the vibrationproducing apparatus.

Fig. 20 is a diagrammatic view of an arrangement of tension patch as applied to the upper and lower surfaces of a wing-to be tested.

Referring to the drawings, and particularly to Fig. 1, the airplane being tested in accordance with the invention comprises the fuselage I, win-gs 2, and tail portion 3. Connected together and to a pair of jacks J are an upper and a lower beam member B1 and B2, respectively.

Referring to Fig. 5, the beam members are} adjustably connected to the forked upper por-? tion 1' of jacks J by levers 4. Each lever 4 has a plurality of holes 5, 51, and 52 therein for adjustably receiving the connecting pin 6. One end of lever 4 is suitably fastened by means of bolt 1 to the upper beam member B1. The other end of the lever 4 is formed with a semi-circular cut-out portion 8 for pivotally receiving a correspondingly-shaped bearing member 9. The upper end of connecting rod I 0 is rigidly fastened to member 9. The lower end of rod I0 is connected to lower beam member B2 by means of pin II as shown in Fig. 2 or, as shown in Fig. 1, by suitably fastening rod I 0 to cross bar l2, rigidly connected to lower beam member B2.

Referring to Fig. 2, an airplane wing is shown being tested by subjecting it to a lifting or ten sion force on the upper side and a compressive or sustaining force on the lower side. A lifting force is applied to the upper surface by means of lifting patches P, cemented to the upper surface of the wing and connected to the upper beam member by means of a whiifietree or lever system referred to generally as W. Patches P are suitably located on the upper surface of the wing to apply loads to the surface at locations and in amounts to simulate as nearly as possible an actual loading condition. By varying the pivotal connections of the various levers constituting the lever system, patches may be added to or taken away from the lifting force producing'system. The total force to be exerted by each patch is predetermined, and the patch is so located as to apply to the area under its influence a force proportional or equal to the force to which that area is subjected under the actual flight condition assumed for test.

Referring to the arrangement of levers in Figs. 2 and 3, link I3 is pivotally connected by means of bolt l4 to upper beam member B1. Lever I 5 is pivotally connected to link l3 at a location such that the major portion of the lifting force is transmitted to link l6 and the minor portion, to link H. The lifting force transmitted to link Ii is divided by means of lever l8 to links [9 and 20. Lever 2| divides the force from link I9 to links 22 and 23, each of which carries two patches by means of a cross lever 24 (Fig. 3) and patch carrying links 25 and 26. Links 2-3, 29, 30, 3|, and 32 are similar to link 22 in that they each carry a lever corresponding to lever 24 to which are attached a pair of patch-carrying links corresponding to links 25 and 26. All the levers are provided with a plurality of. pin-receiving openings for adjustably connecting the links thereto, permitting a wide selection of lever ratios and a ready adjustment of the lever system. It is readily understood that the amount of force transmitted to each patch can be mathematically calculated, and by selectively connecting the links and levers a predetermined force can be applied to each patch.

By way of example, there is shown in Figs. 6 through 10 an arrangement of patches, together with the links and levers for transmitting the lifting force from the upper beam member to the various patches. These lever arrangements will not be described in detail, it being understood that, similarly to Fig. 2, the levers are so selected and connected as to apportion a predetermined lifting force to the area governed by each patch. It is also to be understood that the lever arrangements are connected to an upper beam member and that compression patches, connected to a lower beam member, are also provided.

Referring again to Figs. 2 and 3, a compressive or sustaining force is transmitted from the lower beam member B2 to the under surface of the wing through lever 33, connectors 34 and 35, levers 36 and 31, and thence to compression patches P1. The link and lever connections of the compression patches to the lower beam member are all pin-connected and, as in the upper force-transmitting system, a plurality of pinconnecting openings are provided for making the system adjustable.

The lifting patch, heretofore referred to generally as P, is illustrated in detail in a preferred embodiment in second embodiment in Figs. 13 and 14.

The patch in Figs. 11 and 12 comprises a portion 38 of sponge rubber or other suitable deformable material of a desired thickness and adapted to be cemented to a surface to be subpressure or lifting force. The sponge rubber portion 38 may be cemented or otherwise bonded directly to the plate 40, as shown in Fig. 12a, but it is preferred to bond an intermediate sheet 39 of tough rubber or rubberized fabric to the sponge rubber and the plate to better tranmit the stress from the surface to which the sponge rubber is attached to the plate. Tough rubber, in one of its most common forms, is raw or unvulcanized. It is naturally of a higher density than sponge rubber. A pair of angle irons 4| and 42 are suitably connected to plate 40 by riveting, electric welding, or the like. A connecting plate 43 has two ends rounded. as at 44 to extend under blocks 45 and 46 fastened to the angle irons by bolts 41 and 48. In the preferred embodiment, the patch is approximately six inches by twenty-four inches and is designed to exert a lifting force of one thousand pounds, although in actual tests a lifting force considerably in excess of this has been developed.

As shown in Fig. 12b, a sheet of tough rubber 6| is cemented to the sponge rubber to better transmit the stress from the sponge rubber to the surface to which the lifting force is to be applied. The patch shown in Figs. 13 and 14 comprises a plate 49, a sheet of tough rubber 50 cemented or otherwise suitably fastened thereto, a rubiected to a negative Figs. 11, 12, and l2a and in a berized fabric member 5!, having integral therewith tabs 52 and 53 adjacent one end and tabs 54-and 55 adjacent the other end. The pair of tabs 52 and '53 extend through an opening 56 in the steel plate 48 and have an opening 51 for receiving a link-connecting pin. Tabs 54 and 55 extend through an opening 58 in the plate and are provided with an opening 59 for receiving a link-connecting pin. Cemented to rubberized fabric member 5| is a sponge rubber sheet 60 to which is cemented a sheet of tough rubber 6|. Sheet rubber layer BI is provided to better transmit the stress from the sponge rubber element 60 to the surface to which a lifting force is to be applied. Likewise, strip 50 is provided to insure a better distribution of the lifting force to the plate-by providing an intermediate bonding member whichtransmits the force to the plate without destroying the bond. It is obvious that, under some conditions of operation of the device, members 50 and SI could be omitted as shown in Fig. 14a. It is also to be understood that members 49, 50, Si, 60, and 6| may be bondedtogether by any suitable means.

As illustrated in Fig. 2, the patch P which is connected to link 29 comprises a stiff plate 40a having a concave face 40b conforming approxi mately to the curvature of the adjacent portion of the skin of the aircraft to be tested. A body of resilient rubber material 38a adheres to the concave face 40b of the plate 40a. and it has an opposite face 38b, which is adapted to adhere throughtout its face to the adjacent skin of the aircraft. The resilient body 38a is of substantially uniform thickness and yieldability throughout the area of the face thereof.

Referring to Fig. 15, a lifting patch P is shown cemented to wing 2 which has wrinkled or buckled under applied stress. The buckling is shown slightly exaggerated at 62. This illustrates how the patches permit the surfaces to deform under stress. In order to permit the aircraft skin to deform in waves during the application of the test loads due to shear stress similar to the winkling or buckling of the skin on, for example, a wing due to flight loads, it is essential that the deformable resilient material of the patch be sufficiently thick that the face of the patch cemented to the aircraft skin can deform without interference by the backing-plate of the patch. Tests conducted with various patch constructions have indicated that so long as material has a total thickness of at least one-half inch, the backing plate will be ineffective to locally reinforce the aircraft skin and the skin and the face of the patch adhered thereto will be free to buckle or wave as a result of shear stress in the skin.

Referring to Fig. 16, the jacks are interconnected for pneumatic operation by a system of conduits 63 through 19 to a common source of pressure. invention, no pressure regulating means are provided in any of the conduits, it being the inten tion to vary the lifting force on the surfaces by changing the lengths of the levers or their points of pivotal connection. However, it is to be understood that pressure-regulating valves may be incorporated in portions of the line if desired. As shown in Figure 1'7, means are provided in the conduits for controlling the pressure to the various jacks and, consequently, the force exerted by the various jacks. In this figure of drawing, line 63a, connected to a source of energy (not shown) is divided into lines Ila, 63b and 630. Line Ila conveys pressure to jack J2 through line 12a, and jack J3 through line 13a. Lineflb connects with line 64a, which in turn is connected to lines 68a, 69a, 10a, 14a, 15a, and 16a. Line 630 connects with line 64b, which in turn is connected with lines 65a, 56a, B'Ia, 11a, 18a, and 19a. Pressure-regulating valves V and pressure indicating gauges G both of conventional construction, are provided at desired locations. It is also to be understood that the jacks may be operated by other means, for instance, such as screws, hydraulic means, or otherwise. As shown in Figure 18, jacks of the type illustrated by Jo may rethe layer of resilient In the preferred embodiment of the i place the jacks illustratedin Figure 16. Jack Js is of the screw type in which sliding element J9. is threaded at its lower end at Hi3, Ring I02, rotatably mounted on cylindrical housing I04 of jack Ja is internally threaded (not shown) to operatively engage threaded portion I03. Ring I02 is externally threaded for engagement with pinion ml integral with operating shaft H10. Shaft we is rotatably mounted in bracket m5 and is provided with a thrust collar I06 integral with the shaft for preventing relative longitudinal movement between the shaft and the bracket. The arrangement of the invention illustrated in Figure 16 may be used in connection with hydraulic means as well as pneumatic.

Loads are applied to the plane to represent each and every load on the plane under the conditiont assumed for test. These loads may be all applied by means of the patches, levers, and beams; but it is sometimes found to be more convenient to apply the loads to certain areas by means of weights, such a metal bars or bags of sand or shot. The tail load is applied to the plane: in Fig. 1 by means of bags of shot 85 and 86. The pilot and other loads may be similarly applied. Referring again to Fig. 1, jack J2 applies to the fuselage through lever 80, post 8|, and connection 82, a load representing the engine load. A load representing the gas tank load is applied through jack J3, lever 83, and a post 84. Also,-as previously explained, when testing under conditions other than that of basic load, a load is applied to the fuselage of the plane generally by means of Weights to provide a ing condition, a reaction 'load fuselage, of such a magnitude is applied to the as to permit forces to be applied to the wings and other parts of the plane to stress it in the same manner as the plane would be stressed under the special loading condition. The reaction load is varied to conform to the applied load under the conditions for which the plane is being tested.

Referring to vibration test.

vibration effect, representing a condition to which the plane might be subjected, is applied at a is produced by motor 81, flexible shaft 88 and vibration-producing mechanism 89, suitably attached to the fuselage. The vibration mechanism is old and well known per se and as shown in Figure 19 broadly comprises two oppositely rotating disks H0 and Hi geared to be driven by the motor and flexible shaft and eccentrically H3 to produce vibratory trestlework 90.

The airplane may be tested by means of this downward reac- V apparatus under one or more of several loading conditions. For instance, standard conditions are: high incidence, low incidence, maximum stabilizer and elevator load, maximum fin and rudder load, level landing, three-point landing and nosing over. Special loading conditions include that of inverted flight. The usual tests are under the conditions of high incidence, low incidence, and inverted flight. Also, vibration tests may now be performed following the teachings of the invention.

The operation of the device is as follows:

The jacks are appropriately placed and upper and lower beam members connected thereto by means of rod l0 and lever 4 adjusted to desirably proportion the load between the upper and lower beams. Patches, operatively engaging the sur faces to be stressed, are connected by links and levers to the beam members in such a manner as to transmit the desired amount of force to each patch. Jack J2 is appropriately connected to exert on the plane a load representing the engine load. Jack J: is appropriately connected to the fuselage to exert thereon a load representing the gas tank load of the plane. action load is opposed to plane and may be applied to the fuselage by jacks and patches or by weights. Pilot, tail surface, and other loads are also applied to the plane,

For instance, if

choring the lower beam system, thereby permitlower. Adynamometer I beam system than by the i II of conventional construction is provided in connection with the anchorage of the lower beam system, it being understood that such dynamometersmay be used in the system wherever desired. When testing for the condition of inverted flightpthe airplane is inverted and compression patches are applied to the uppermost, and tension patches to' the lowermost surfaces of the wings. The fuselage is suitably supported, and the beams and lever to which the patches are connected are so arranged as to produce downward forces on I said wings.

It is to be clearly understood that description in the specification and drawings is by way of illustration only and is not to be taken in any way as limiting the spirit and scope of the invention. It is intended to be limited only by the terms of the appended claims.

We claim:

1. Apparatus for applying test loads to structures subjected under a condition of operation to positive and negative pressures, comprising jacks operatively connected to a common source of power, upper and lower beam members, a linkage system for connecting an upper and a lower beam member together and to said jacks, means adapted to adhere to a surface of said structure which is subjected to negative pressure and connected to one of said upper beam members to exert a tension force on said surface, and means engaging a surface of said structure subjected to positive pressure and connected to one of said lower beam members to exert a compressive force on said surface.

2. A device as recited in claim 1 in which said linkage system is adjustable to change the ratio of the forces exerted beams. I

3. Apparatus for applying test loads to structures subjected to positive and negative pressures,

by the upper and the lower comprising force-transmitting members operatively connected to a common source of power, upper and lower beam members, means connecting certain of said upper and lower beam members together and to certain of said force-transmitting members, lifting patches connected to each of said upper to adhere to surfaces to negative pressure, compression patchesv connected to each 01' said lower beam members and adpated to engage surfaces of said structure iected to positive pressure and means connected to other force-transmitting members and engaging said structure to apply loads thereon.

4. Apparatus for applying loads to an aircraft structure, comprising operatively connected force-transmitting members, pairs of upper and lower beam members, linkages connecting the ends of each pair of upper and lower beam members to a pair of said force-transmitting members, said linkages being adjustable to change the ratio of forces transmitted fromthe force-transmitting members to the upper and lower beam members, lifting patches connected to each of the upper beam members and adapted to adhere to a surface of said structure in such a manner that the force exerted by each patch corresponds to the force to which the areav governedv by the patch is subjected during the flight condition assumed for test, elements connected to each lower beam member for exerting a compressive force on areas subjected to such a force dition, and additional force-transmitting members operatively connected with the first-named beam members and adaptedof said structure subjected subduring said flight coni characteristics and force-transmitting members and with the structure for exerting loads on the structure representing engine, gas tank, pilot, and other loads.

5. A lifting patch for transmitting forces to a structure the strength .of which is to be tested. comprising a relatively rigid plate member having slots therein, a rubberized fabric element bonded to said plate member and having tabs extending through said slots and a member of deformable material bonded to saidelement and adapted to be adhesively connected to a surface of said structure, said member of deformable material being of such a thickness as to transmit throughout its area substantially uniform stress to offer negligible resistance to such deformation.

6. A device as recited in claim Sand further including a relatively thin stress-transmitting member bonded to said member of deformable material and adapted to be adhesivelyattached' to said surface of said structure.

'1. A laminated lifting patch for transmitting forces to a structure, the strength of which is to be tested and which structure is subject to surface deformation under stress, comprising a relatively mitting member between said member of deformable material and said surface said thin member being deformable material and adapted to be adhesively attached to said surface of said structure.

9. Apparatus for static testing a suitably enclosed airplane structure, comprising means for partially supporting the load of said structure by subjecting the upper surface thereof to an external tension force, said means including a tension patch comprising a relatively rigid member and a member of deformable material bonded to said member and adapted to be adhesively connected to a surface of said structure, said member of deformable material being of such a thickness as to transmit throughout its area substantially uniform stress characteristics and to offer negligible resistance to deformation of said surface, means applied to the under side of said of said structure,

structure for supporting the residual load thereof, and means for correlating the action of said ing the wing, applying an adhesive lifting patch to the upper surface thereof, applying a compressive patch to the lower surface thereof, subjecting the patches to predeterminatelyproportioned upward lifting forces to stress the wing through the medium ofthe patches, and measuring the deflection of the wing when stressed.

11. Apparatus for static testing an aircraft structure, comprising means for suitably anchoring the aircraft structure, means for producing a predetermined lifting force on the. upper surface thereof, including a lifting patch composed of a rigid backing plate and a layer of elastic material adapted to be cementitiously attached to bonded to said member of said upper surface, means including a patch of elastic material for applying a predetermined lifting force to the under surface of said structure, and means for producing a vibratory force on a selected part of said structure.

12. The method of testing an airplane wing for a given flight condition comprising suitably anchoring the wing, applying adhesive lifting patches to the upper and lower surfaces of the wing in predetermined positions according to the stresses desired to be transmitted thereto, subjecting the patches to p'redeterminately proportioned wing-stressing lifting forces, and measuring the deflection of the wing when so stressed.

13. A loading patch structure for the stresstesting of aircraft, said patch structure comprising a stiff plate having a concave face conforming approximately to the curvature of the portion of the skin of the aircraft to be tested, and a body of resilient rubber material adhered to the concave facelof said plate and having an opposite face adapted to be adhered throughout said face to the skin of the aircraft, said body being of substantially uniform thickness and yieldability throughout the area of said face thereof.

14, A loading patch structure for the str sstesting of aircraft, said patch structure comprising a metal plate, a body of sponge rubber at a face of said plate, a layer of dense rubber material between said plate and said body of sponge rubber and united to said body, and a uniting material between said dense rubber layer and said plate, said uniting material comprising a suitable cement, and said structure having a face opposite said plate adapted for adhesion to the skin of the aircraft.

15. A loading patch structure for the stresstesting of aircraft, said patch structure comprising a metal plate, a body of sponge rubber at a face of the plate. a layer of dense rubber material interposed between said body and said plate and adhered to both, and a layer of dense rubber material at the opposite face of said body and adhered thereto, the last said layer of dense rubber material having a face adapted for adhesion throughout said face to the skin of the aircraft.

16. Testing apparatus for static testing a hollow aircraft structure such as a wing having a load-transmitting covering forming opposite surtested, an elastic patch adhesively bonded to each covering surface throughout the entire area of the patch contiguous with the surface and each patch extending laterally from the plane of load application of said rigid members, a load-transmitting connection between each of said load-transmitting member and a respective patch, and means for simultaneously applying apportioned loads to said rigid members in the same direction.

17. Apparatus for static testing an aircraft structure by subjecting the aerodynamic lifting surfaces thereof to a distributed loading simulating on of the flight conditions of the aircraft, comprising adhesive elastic tension patch means for exerting a first lifting force distributed over a substantial part of the surface subjected to negative pressure, elastic compression pad means for exerting a second substantial part of the surface subjected to positive pressure, and load applying means intercon-. necting said patch and pad means and so constructed as to maintain a predetermined ratio relationship between the first and second lifting forces.

18. An apparatus for applying test loads simulating air loads to an aircraft structure through opposed skin portions of the structure comprising' a frame surrounding th structure and adapted to be elevated with a known force in planes normal to the opposed skin portions of said structure, said frame including at least two rigid backing members each respectively contiguous with one of said opposed skin portions, and elastic deformable patches of uniform thickness cemented throughout one of the faces thereof to a respective one of said opposed skin portions and the opposite faces of said patches being cemented to said backing members, said frame and patches being constructed and arranged such that elevation of said frame causes application of a distributed tension load normal to one skin portion and a distributed compression load normal to the opposed skin portion having a predetermined ratio to the magnitude of the dis tributedtension load.

19. A testing system for applying loads -.to,an

' aircraft wing to simulate at a particular wing chord station the effects of the negative and positive air pressure loads occurring in flight on the upper and lower surfaces of the wing over an area extending spanwise on each side of the said wing chord station, comprising a pad of resilient material having a uniform thickness of the order of one-half inch or more adhesively bonded throughout its lateral area to the upper surface of the wing and extending spanwise on either side of the said wing chord station, a similar pad of resilient material secured to the under-surlifting force distributed over a face of the wing and extending spanwise on either side of the said wing chord station, upper and lower rigid backing members each bonded to a respective one of said pads to distribute loada from the backing members uniformly over the area of the pads, and means for applying predetermined apportioned loads simultaneously to each of said backing members in the same direction to apply load to the upper surface through one pad simulating the effect of negative airpressure load thereon and to apply load to the lower surface through the other pad simulating the effect of positive air pressure load thereon.

20. A testing system for applying test loads to an aircraft wing structure or the like when arranged in a normal flight attitude comprising upper and lower beam members disposed respectively above and below the wing at a selected wing chord station and parallel to the wing chord, a pair of fluid pressure jacks, each Jack having a link adjustably fulcrumed on the load supporting member of the Jack intermediate the ends of the link, tension rods connectin one end of each link to the upper beam member, tension rods connecting the other ends of the links to the lower beam member, simultaneous actuation of said jacks causing a predetermined apportionment of the total load between said upper and lower beam members, separate load-dividing linkage systems respectively operatively connected with said upper and lower beam members, a plurality of elastic tension patches adhesively bonded to the upper surface of the wing and extending spanwise of the plane of said wing chord station,

to the under-surface of spanwise of the plane of individual rigid backing tension and compression iormly over the area of each patch, tension-load transmitting connections between the tension patch backing plates and the load dividing linkage associated with the upper beam member and separate compression load-transmitting connections between the backing members of the compression patches and the lower beam member.

21. The structure as claimed in claim 20, in which both the tension and compression load ap-- plying patches are arranged on the upper and lower surtaees of the wing in a plurality of rows extending spanwise and chorwlse of the wing on either side of the said wing chord station point and each of the load-dividing linkages havin means for apportioning the loads transmitted from the respective beam members to the respec-- tive spanwise rows of patches in a predetermined manner and said load-dividing linkages havingfurther means for apportioning the load between the respective patches in each spanwise row of patches.

'PAUL H. KEMMER.

EDGAR R. WEAVER. 

